In certain applications it is desirable to support a load in such a manner that the support is relatively rigid during normal operation. An example is equipment such as an antenna system for a radar installation, but other examples include buildings, structures, or other equipment. In normal use, a platform supporting the antenna is expected to provide a relatively rigid load path to the ground. Such a support is desirably relatively rigid in order to stabilize the structure for optimum performance and accuracy. Rigid supports, however, can cause damage to the supported structure in the event of violent shaking or vibration such as may be experienced during a seismic event.
In the past, vibration or motion isolations have generally acted merely to isolate the load or a platform supporting the load from anticipated vibration. Examples of such isolations are found, for example, in the inventions of U.S. Pat. No. 5,803,213, U.S. Pat. No. 5,918,865, and U.S. Pat. No. 5,947,240, all of which are assigned to the assignee of the instant invention. Each of the noted patents relates to load isolation from vibration and each utilizes air suspension springs which are damped by cross-connecting conduits to and from a pair of isolation struts.
While these devices provide vibration isolation for, for example, isolating a payload from a launch vehicle, they are not intended to provide relatively rigid support for the payload in a first mode of operation and less rigid but damped support in another mode of operation. They are intended, rather, continuously to provide isolation from vibration at all times.
The devices of the above-identified patents comprise a plurality of load isolation struts, each strut having a pneumatic cylinder, or air suspension spring, with a piston dividing the cylinder into two chambers, and a hydraulic cylinder with a second piston dividing the hydraulic cylinder into two chambers. The air suspension spring provides isolation from vibration and the hydraulic cylinder provides damping of the resulting oscillation of the air spring during vibration.
Isolation systems incorporating the above devices may comprise pairs of struts placed around the supported load, each strut having its respective hydraulic cylinders cross-coupled to the cylinders of the other strut of the pair.
While this arrangement is effective in isolating a load from vibration and for damping the effects of any such vibration, the system is intended to operate continuously in the vibration isolation and damping mode.